MMBT4124-7 Equivalent & Substitute Parts

Part Overview

The MMBT4124-7 is an NPN bipolar junction transistor manufactured by Diodes Incorporated in SOT-23-3 surface mount packaging. This device is rated for 25 V collector-emitter breakdown voltage, 200 mA maximum collector current, and 300 MHz transition frequency. The part is classified as obsolete, necessitating identification of active equivalent and substitute components for new designs and ongoing production requirements. Multiple manufacturers offer functionally compatible alternatives in the same package family with comparable or enhanced electrical characteristics.

Key Parameters

Parameter	Value	Unit
Transistor Type	NPN	—
Voltage - Collector Emitter Breakdown (Max)	25	V
Current - Collector (Ic) (Max)	200	mA
Power - Max	300	mW
Frequency - Transition	300	MHz
DC Current Gain (hFE) (Min) @ Ic, Vce	120 @ 2mA, 1V	—
Vce Saturation (Max) @ Ib, Ic	300mV @ 5mA, 50mA	—
Operating Temperature Range	-55 to 150	°C
Package / Case	SOT-23-3 (TO-236-3, SC-59)	—
Mounting Type	Surface Mount	—

Substitute Part Grouping Explanation

Substitution of the MMBT4124-7 is determined by strict adherence to the following electrical and mechanical parameters:

Primary Substitution Criteria:

Transistor type must be NPN
Collector-emitter breakdown voltage must be greater than or equal to 25 V
Maximum collector current must be greater than or equal to 200 mA
Package must be SOT-23-3 (TO-236-3, SC-59) surface mount
Operating temperature range must encompass -55°C to 150°C

Secondary Compatibility Factors:

Transition frequency of 300 MHz or higher preferred for direct replacement
DC current gain (hFE) minimum of 120 or greater at specified test conditions
Vce saturation characteristics suitable for switching applications

Substitute parts are grouped into two categories based on electrical performance:

Category A - Direct Electrical Equivalents: Parts maintaining identical or near-identical electrical specifications (MMBT4124LT1G, MMBT6429LT1G)

Category B - Enhanced Performance Substitutes: Parts exceeding the original specifications in collector current capacity, voltage rating, or frequency response while maintaining package compatibility and temperature range (BC818-40LT1G, FSB649, KSC3265YMTF)

Category C - Voltage-Rated Alternatives: Parts with higher collector-emitter breakdown voltage suitable for applications requiring increased voltage margin (MMBT2484LT1G, MMBT2484LT3G)

Parameter Comparison

Part Number	Manufacturer	Vce(BR) Max (V)	Ic Max (mA)	Power Max (mW)	fT (MHz)	hFE Min @ Ic, Vce	Package	Product Status	RoHS Status
MMBT4124-7	Diodes Inc.	25	200	300	300	120 @ 2mA, 1V	SOT-23-3	Obsolete	Non-compliant
MMBT4124LT1G	onsemi	25	200	225	300	120 @ 2mA, 1V	SOT-23-3	Active	ROHS3 Compliant
MMBT6429LT1G	onsemi	45	200	225	700	500 @ 100µA, 5V	SOT-23-3	Active	ROHS3 Compliant
BC818-40LT1G	onsemi	25	500	225	100	250 @ 100mA, 1V	SOT-23-3	Active	ROHS3 Compliant
FSB649	onsemi	25	3000	500	150	100 @ 1A, 2V	SOT-23-3	Active	ROHS3 Compliant
KSC3265YMTF	onsemi	25	800	200	120	160 @ 100mA, 1V	SOT-23-3	Active	ROHS3 Compliant
MMBT2484LT1G	onsemi	60	100	225	—	250 @ 1mA, 5V	SOT-23-3	Active	ROHS3 Compliant
MMBT2484LT3G	onsemi	60	100	225	—	250 @ 1mA, 5V	SOT-23-3	Active	ROHS3 Compliant

Engineering Selection Recommendations

For Direct Replacement in Existing Designs:

MMBT4124LT1G is the primary recommended substitute. This part maintains identical electrical specifications to the MMBT4124-7 across all critical parameters: 25 V breakdown voltage, 200 mA collector current, 300 MHz transition frequency, and 120 minimum hFE. The part is manufactured by onsemi, carries active product status, and is ROHS3 compliant. Inventory availability is substantial at 24,400 pieces. This substitution requires no circuit redesign.

For Enhanced Performance Applications:

MMBT6429LT1G provides superior frequency response (700 MHz) and higher DC current gain (500 minimum hFE) while maintaining the 25 V voltage rating and 200 mA current capacity. This part is suitable for high-frequency switching applications and RF circuits. ROHS3 compliance and active status are confirmed.

For Increased Current Capacity:

BC818-40LT1G and FSB649 accommodate higher collector currents (500 mA and 3 A respectively) within the same SOT-23-3 package. Both maintain 25 V breakdown voltage and are ROHS3 compliant with active product status. FSB649 additionally provides 500 mW power dissipation. These parts are appropriate for applications requiring higher current handling without package change.

For Voltage-Margin Applications:

MMBT2484LT1G and MMBT2484LT3G offer 60 V collector-emitter breakdown voltage, providing increased voltage margin for circuits operating near the 25 V limit. Both variants are ROHS3 compliant and active. The LT3G variant is available in higher quantity (30,428 pieces) compared to LT1G (9,200 pieces). These parts are suitable for applications requiring voltage derating or operation in higher-voltage environments.

Compliance Considerations:

All recommended substitutes are ROHS3 compliant, addressing the non-compliant status of the original MMBT4124-7. All parts maintain AEC-Q101 automotive qualification or equivalent reliability standards. Moisture sensitivity level remains at MSL 1 (Unlimited) across all alternatives.

Frequently Asked Questions (FAQ)

Q: Can MMBT4124LT1G be used as a direct drop-in replacement for MMBT4124-7?

A: Yes. MMBT4124LT1G is electrically and mechanically identical to MMBT4124-7. Both devices share the same 25 V breakdown voltage, 200 mA maximum collector current, 300 MHz transition frequency, and SOT-23-3 package. No circuit modifications are required. The primary difference is product status (active versus obsolete) and RoHS compliance.

Q: What is the difference between MMBT2484LT1G and MMBT2484LT3G?

A: Both parts are electrically identical with 60 V breakdown voltage and 100 mA collector current. The difference is packaging: LT1G is supplied in Cut Tape (CT) & Digi-Reel format, while LT3G is supplied in Tape & Reel (TR) format. LT3G has higher inventory availability (30,428 pieces versus 9,200 pieces). Selection depends on procurement and assembly requirements.

Q: Why would I choose FSB649 over MMBT4124LT1G if both have 25 V ratings?

A: FSB649 is selected when the application requires higher collector current capacity (3 A versus 200 mA) or greater power dissipation (500 mW versus 225 mW). The SOT-23-3 package remains identical, enabling board-level compatibility. FSB649 is appropriate for power switching applications where the original 200 mA specification is insufficient.

Q: Is MMBT6429LT1G suitable for all applications using MMBT4124-7?

A: MMBT6429LT1G is suitable for applications where the higher transition frequency (700 MHz versus 300 MHz) and increased DC current gain (500 minimum hFE versus 120 minimum hFE) do not create circuit instability. The 45 V breakdown voltage exceeds the original 25 V specification, providing additional voltage margin. Applications operating at or near the frequency limits of the original part benefit from this substitution.

Q: What packaging options are available for these substitutes?

A: All substitute parts are supplied in SOT-23-3 (TO-236-3, SC-59) surface mount packaging, maintaining mechanical compatibility with the original MMBT4124-7. Packaging variants differ in tape format: Cut Tape (CT) & Digi-Reel, Tape & Reel (TR), or both. These differences affect procurement and assembly processes but do not impact electrical performance or board-level compatibility.

Q: Are all substitute parts RoHS compliant?

A: Yes. All recommended substitute parts carry ROHS3 compliance status. The original MMBT4124-7 is RoHS non-compliant. Substitution with any recommended alternative addresses RoHS compliance requirements for new designs and production transitions.

Q: Can MMBT2484LT1G or MMBT2484LT3G be used in circuits designed for 25 V operation?

A: Yes. MMBT2484LT1G and MMBT2484LT3G are rated for 60 V collector-emitter breakdown voltage, which exceeds the 25 V requirement. These parts operate safely in 25 V circuits and provide additional voltage margin. However, the maximum collector current is reduced to 100 mA, which may be limiting in applications requiring the original 200 mA specification.

Q: What is the significance of the DC current gain (hFE) differences among substitutes?

A: DC current gain determines the base current required to achieve a specified collector current. MMBT6429LT1G has the highest minimum hFE (500), requiring the least base current for saturation. MMBT4124LT1G and the original MMBT4124-7 have identical hFE (120 minimum). FSB649 has the lowest hFE (100 minimum). Circuit designs using fixed base resistors may require adjustment if substituting between parts with significantly different hFE values.

Q: Is inventory availability a factor in selecting a substitute?

A: Inventory availability is a practical consideration for procurement planning. MMBT6429LT1G has the highest inventory (155,200 pieces), followed by MMBT2484LT3G (30,428 pieces) and MMBT4124LT1G (24,400 pieces). Lower inventory parts such as MMBT2484LT1G (9,200 pieces) or FSB649 (1,520 pieces) may have longer lead times. Selection should balance electrical requirements with supply chain constraints.

Request Quote (Ships tomorrow)

Part Number

Quantity

Company

Contact Name

E-mail

Message